Stabilized silver halide emulsions



Patented Apr. 20, 1948 N OFFICE STABILIZED SILVER IIALIDE EMULs'IonS Fritz W. H. Mueller, Binghamton, N. Y., asslg'nor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application September 16, 1944, Serial No. 554,539

6 Claims.

This invention relates to the improvement of photographic emulsions and more particularly to the incorporation of antifogging or stabilizing agents into silver halide emulsions.

A large number of substances have been described as being effective in preventing an in-. crease in fog and thus stabilizing or controlling the keeping quality of photographic emulsions. Many of these stabilizers have definite limitations in their ability to produce desirable effects without producing unfavorable side reactions. Thus, some stabilizers desensitize or produce fog, when added during the mixing or ripening, but exert favorable effects when added to the melted emulsion before coating. It is one object of this invention, therefore, to produce a stabilized emulsion of improved photographic quality while incorporating the stabilizing agents over a wider range of application during the manufacture of photographic emulsions. I

In U. S. Patent 2,057,764 there is described a process of stabilizing photographic silver halide emulsions by incorporating sulfinic or seleninic acids or their salts into the emulsion in theform of a solution in a suitable solvent during the preparation of the emulsion or by incorporating the stabilizer into the finished emulsion by bathing the emulsion layer with a weak solution of the stabilizer. It is stated that the fogging influence f supports, preparation layers, backing layers, iintermediate layers, sublayers, protective layers,

or baryta layers could be prevented by incorporating these stabilizers into such layers. As compared with films which were not provided with the sulfinic acid or seleninic acid stabilizers, it is thionates, preferably those containing a total of three or more sulfur atoms and th'ioanhydrides of sulfonic acids containing a total of three or more sulfuratoms will improve the stabilization characteristic of photographic emulsions containing asulfinate or seleninate to an extent unobtainable with the sulfinate or seleninate treatment. The remarkably improved result is manifested in a reduction of the fog density to approximately 50 of that obtained when using sulfinate or seleninate alone. Thus, films having a fog density of to density units after having added sulfinate are reduced to a fog density of 12 to 15 density units by adding small amounts of a polythionate or thioanhydride.

This reduction in fog density produces a better clearness, better keeping quality and an unusual brilliance which is especially desirable in medical and industrial radiographs. Concentrations of 0.025--0.500% by mol of the polythionate or thioanhydride compounds to the sulfinates or seleninates are suflicient to produce this reduction in fog density. Suitable polythion'ates and thioanhydrides which will produce this desirable effect can be considerably improved and the range of formula M0sO2Sn-SO2OM wherein M is an alkali metal or hydrogen and n I is a positive integer, or of the thioanhydrides of sulfonic acids of the formula wherein R is an organic radical and n is a positive integer, are present in the emulsions containing the sulfinates or seleninates. It has been obwhen used in combination with a sulfinate or seleninate include such compounds as sodium trithionate, sodium tetrathionate, potassium pentathionate, potassium, hexathionate, dibenzene sulfonyl mono-, di-, tri-, and tetrasulfide.

'Polythionates have been used in silver halide emulsions without sulfinates or seleninates'for the production of photographic elfects .wherein the polythionate is employed as a ripening substance, that is, a. substance capable of enhancing the photographic speed. Such a. process is described in U. S. Patent 1,673,522. It is interesting to note that this use of polythionates for enchancing the sensitivity of the emulsion is usually accompanied by adefinite loss of clearness. It is, therefore, surprising that polythionates exert a fogpreventing or anti-ripening or stabilizing action when used in combination with sulfinates or seleninates.

The polythionates or thioanhydrides, which produce this increased stabilization, can be formed in the solution of the sulfinate or seleninate by reaction between some of the sulfinate or seleninate and colloidal sulfuradded to the sul finate or seleninate solution, or nascent sulfur or selenium producedbycatalytic decomposition of a suitablelabile sulfur compound such as sodium thiosulfate which hasibenadded' to thejsulfinate or selenlnatesolution. This invention, therefore, contemplates and includessuch formation of the served that extremely small quantities of polyo5 polythionates or-thioanhydrides.inthesulfinate limited to. any nartic which exerts the 'hh anidaoe thionanhydrides are then formed in the sulfinate Y or seleninate solution in accordance with the following mechanism: a

III. iRSSR ZNazS GNaOH wherein R is an organic radical, n is a positive integer, and the sulfur maybe replaced by seen um Thus as a specificeXam-ple, sodium benzene sulfinate plus sulfur yields sodium benzene thiosulionate (Equation #1). Thissodium benzene thiosulfonatefurther reacts with sulfur to form the thioanhydrides, -'dibenze ne sulfonyl polysulfides (Equation #11). The-by-productsare diphenyl disulfides and sodium sulfide. The diphenyl disulfide iurther'reacts to fqrmthiophenol and sodium thiosulf ate Equation III), whichflatter can be easily Qxidized tosodium olythionate (Equation IV). The sodium thiosulfate may, of course, be added assuch tothe sulfina'te or seleninate solution and be dil'dtly oxidizedftosodium polythionate. 'In eithericase, any suitable o i izin cata yst may.bieem ?yed,u Salts of rsenic, tin and an imony I have o served that u h catal sts may also acceler t e OX elation to olythi nates ofthi sulfui e acid ester al in a kali.' ,1'e."sQ. l Jt "s entnio' uric a ester sa s a idrfi'ns nee, phe 'yl thi su f id ester'sodiumsalt brs all amoun iithiosulfatesor cdmnli l'ldsq often be' resent. in'teiclinical rades o 'su flna re ardless of new the sulfinate n siheen p pared. In order toiihprove such technicfaijgrades of sulfinates or selehin'a'tes'ior'the'purpose,ofiog prevention in hotographic emulsions and at the sa'm'e'ti'm'e to el minat" 'thetime consuming nd expensivefirccedureor. c mical purifi atio and recrystallizationone' ofthd 1 ve mentioned ca y u h as idm f nitehr a mixture t arsenic andftin salts; ma be added to'theisulfinates during the "maniifejdture' oi the su fi lates or seleninates or oft "e emanate 'or seleninate l t s be 'dre lisi athfe latter with photora hic emtlsms. 'Sdlhe' thf a1 era. s of s fi ates which remain iIfiDl itifesfor by-produc s which can b easily' b d fz'd to polythijon'ates can be improved by aaai'n'gasmauammnt of a mild oxidizing agent such as potassium 'ier'ricyi e- 3 i v V without ny vies 1W? by the holythionates n'cl'thi be ieve th t h ss bili'zjaticnl is-eitht a dlyt d one. or, int rac on betwee' the polyt hydrides and the snlfir ate's or ,se mnates w t the hd s ble 'n odutidn di a. [reaction T produ t I {e321 statnizmemfiueme On the silver halide emulsion; The "following ex-' 'ar str t ures may 4 .7 amples will serve to further illustrate the inven tion, it being understood that the invention is not limited thereto.

Example I To -one kilogram of melted gelatino-silverhalide emulsion containing from 6 to "1% of silver halide and approximately 8% gelatin, there were added during ripening:

'15 cc. of a 20% solution of the sodium salt of "ben ene, sulfinid acid in Water and 1 cc, of potassium pentathionate of a concentration of-one gram per liter in water.

were made with the same silver halide emulsion-but without the addition of either the sodium'salt of benzene sulfinic acid or the potassium pentathionate. Additional similar test films were made with the same silver halide emulsion to whioh had been added during ripening the same quantity of the sodium salt of benzene sulfinic acid as above, but omitting the potassium pentathionate. v

The fog density of eachof these types of test film was determined for the freshly prepared film and test pieces of each type were then incubated for six days at 50 C. It was observed that the fog density or the films treated with benzene sodium sulfinate solution to which had n ad e ssium. n n et d te' was creased by 50%, in the case of the freshly preparedfilm, and about 45%, in-the case of the incubated film, 0f the fog density of the films which had been treated only with sodium benzene sulfinate.

E ample II To one kilogram of melted gelatino-silverhalide emulsion containing from 6 to 7% silver After ripening the emulsionwas-cast-on'a film b'aseand out into test film lengths.- Similar test films were-made of the silverhalide emulsion but without the-"addition oi' either of the sodium'salt of benzene seleninic afcid'or -the sodium tetrathionate. Additional similar'te's't ;filrrlsjwere also made with the same silver halide emulsion to which was added fthesame quantity of the sodium saltof benzene seleninic acid as'above, but omitti g thespdium tetrathionate'l V Theyfog'density-"Oran three types :of these test films was "determined forthe freshlyprepared film andthe remaining test-lengths of each type 0t test filmlwere then incubated for a period of six days at a temperature'offi'Q fC. {It {wasobserved that the fog density 'of thefilms-treated with sodium benzene seleninate solutionto'whioh had been added sodium tetr th w d creased by 5.0%, in the case of the freshly :pre-

'p'areicl'film, and'about 4 in he p asei f the Example III od u enzene ulfina'te was prepar a mom ing to the process "outlined by Gatterm ann in Berichte 32, 114011899).

. '5 '200grams of the crude sodium salt of the benzene sulfinic acid thus obtained were dissolved in one liter of water.

0.25 to 1 gram of sodium arsenite were added. This solution was allowedto stand at room temperature for 24 hours.

A similar solution of the crude sodium salt of the benzene sulfinic acid and water but omitting the addition of sodium arsenite was made up and also allowed to stand at room temperature for 24 hours.

The two solutions were then added to gelatinosilver-halide emulsions in amounts from 5-20 cc. per one kilogram of emulsion during the ripening stage. Similar amounts of the two benzene sulfinate solutions may be also added to silver halide emulsion before coating as a coating final.

Test strips of the films thus produced were examined for fog density when freshly prepared and other test strips of the same films were incubated for a period of six days at a temperature of 50 C. and then examined for fog density.

Example IV Sodium benzene sulfinate was prepared in accordance with the process outlined by Knoevenaegel et al. in Berichte 41, 3318 (1908).

0.1 gram of potassium ferrioyanide was added to one liter of a solution of the crude sodium benzene sulfinate thus prepared. This solution was allowed to stand for '72 hours, then filtered.

1 liter of a 20% solution of this crude sodium benzene sulfinate omitting the addition of potassium ferricyanide was also allowed to stand for '72 hours and filtered.

Samples of each of these solutions were then added to melted gelatino-silver-halide emulsions in amounts of 5 to 20 cc. of the sulfinate solution per 1 kilogram of emulsion during the ripening stage. Similar amounts of the same sulfinate solutions may be also added to a silver halide emulsion before coating as a coating final.

Test strips of the films when freshly prepared were examined for fog density. Additional test strips of these films were then incubated for a period of six days at a temperature of 50 and again tested for fog density.

It was observed that the fog density of the films treated with the sodium benzene sulfinate to which had been added potassium ferricyanide was improved to about the same extent as in the case of the preceding example as compared with the fog density of the films which had been treated with the blank sulfinate solution.

Example V Sodium benzene sulfinate was prepared according to the process outlined by Smiles et al. in Qrganic Syntheses Coll. vol. I, page 7 (1932). The sodium benzene sulfinate thus prepared was recrystallized and made up into a 20% solution with water.

0.1 gram colloidal sulfur was added to one liter of the 20% solution of recrystallized. sodium benzene sulfinate.

The colloidal sulfur addition was kept in suspension by stirring for 48 hours at room temperature.) The temperature was then raisedto 46 6. for. one hour and the solution filtered.

Samples of this solution of the sodium benzene sulfinate treatedwith colloidal sulfur and samples of a 20% solution of the same recrystallized sodium benzene sulfinate which had not been treated with the colloidal sulfur were added to a wmelted gelatino silver-halide emulsion in amounts of 5 to 20 cc. of the sulfinate solution per 1 kilogram of emulsion duringv the ripening stage. 1 Similar amounts of these same solutions may be also added to gelatino-silver-halide emulsion before coating as a coating final.

Test strips of the films when freshly prepared were examined for fog density. Additional test strips of these films were then incubated for a period of six days at a temperature of 50 and again tested for fog density.

. It was observed that the fog density of the films treated with the sodium benzene sulfinate to which h'adbeen added colloidal sulfur was improved to about the same extent as in the case of the preceding example as compared with the fog density of the films which had been treated with the blank sulfinate solution.

Example VI To 1 kilogram of a. melted gelatino-silver-halide emulsion containing 6 to 7% silver halide and 8% gelatin, there were added during the ripening:

in a concentration of 1 gram per 1 liter methyl alcohol. The clearness of the film was determined in an identical manner as described in Example I. It was observed that the clearness of the emulsion layer treated with dibenzene sulfonyl monosulfide was improved to about the same extent as in the case of Example I, as compared with the same emulsion. to which only sodium benzene sulfinate had been added. It may be mentioned that the dibenzene sulfonyl monosulfide may be substituted by equimolar concentrations of dibenzene sulfonyl di-, triand tetrasulfide with similar results.

Example VII To a gelatino-silver-halide emulsion containing silver halide corresponding to grams silver nitrate there were added 50 cc. of a 20% solution of sodium benzene selem'nate and 25 cc. of a solution of sodium trithionate in a concentration of 1 gram per liter water immediately after the precipitation of silver halide and prior to the surface digestion. The emulsion was washed and after-ripened in a manner familiar to those skilled in the art. The clearness and the keeping quality of the emulsion while depending on the type of gelatin employed was found to be in all cases improved as compared to one obtained with the addition of sodium benzene seleninate without the addition of sodium trithionate to about the same extent as in the case of Example I.

The sodium salt of benzene sulfinic acid and the sodium salt of benzene seleninic acid used in the above examples can be substituted by equimolar concentrations or other sulfinie or seleninic acid salts such as sodium salt-of ethane-sulfinio acid, 'ohlorobenzene sulfinic acid, toluene-p-sulfinic acid, l naphthalehe-suliinic acid, :hexahydrobenzene sulfinic acid andrthib phene-sulfnic acid The potassium pentathioriate andbsodium tetrathionate used in Exa-mplesI and II'ca'n be substitutedby equiniolecu lar concentrations of soluble salts of any thionic acidcompouud's having three or more sulfur atoins such as, for instance, hexathionicacid and any thioanhydride having oneor more central sulfur atoms.

consisting of polythionicjacidsand their salts The improvement obtainable when the fog characteristic is expressed in density units will, of course, vary somewhat depending upon the type of gelatin and the formula used in making the gelatino-silver-l-ialidei emulsion; However, it has been found that the result; as compared with the same film v-treated only with the suifini-c or. seleninic acid salt is invariably a decrease infog density oipapproximately 50% for freshly prepared film and approximately 45% after six days incubation.

What I c1aimasimyinvention and desire to 1 be secured by Letters Patent of the United States 1. A photographic material comprising a silver halide gelatin emulsion; a member of the group consisting of asulfinicacid, a seleninic acid and their salts and a member of the group consisting of polythionic acids and-their salts of the formula Mosoz-sn-sotoixi wherein M is 'a member of theg'roup consisting 'ofalkali metals and hydrogen and is a positive integer, and thioanhydrides of-the rormuia RSO2-'S11SO2R- wherein R isan organic radical and n is a positive integer, in concentrations of from 0.025 to 0500% by inol of the member of the last named group to the mem er of the first named group. 2., A photographicjmaterial comprising a silver halide gelatin emulsion containing a member of thegr-oup consisting of Sulfihi acid, a s'eleninic acid and their salts, and a member of the group of the formula I mosoz-swso't'om wherein .M is a member of the group consisting of alkali metals and hydrogen and n is a positive integer, and thio'anhydrides of the formula RSOFSn-SOR wherein R is an organic radical and 11 1s, a positive integer; in concentrations of from 0.025 to 0.500%. by mol of thememberof thelastnamed group to'the member of the first named group. 3. A photographic material comprising a silver halide gelatin emulsion, a member of the group consisting of a suliinic acid, -a seleninic acid and their salts and a member of the group consisting of dibenzene sulfonyl mono-, di-, tri-, and .tetrasulfide in concentrations of from 0.025170 0.500% by mol of the member of the last named group to the member of the first named group.

t. A photographic material comprising a sil ver halide gelatin emulsion, sodium benzene sulf nate andpotassium pentathionate in concentrations of from 0.025130 0.500% by mol of thepotassium pentathionate to the sodium benzene sulfinate.

5 A photographic material comprising a silver halide gelatin emulsion, sodium benzene seleninate and sodium tetrathionate in concentrations of from 0.025 to 0.500% by mol of the sodium tetrathionate to the sodium benzene seleninate.

6. A photographic material comprising'asilver halide gelatin emulsion, sodium benzene 'sulfinate and dibenzene "su'lfonyl monosulfide in' concentrati'cns of from 0.025 to 0;500% by mol of the dibenze'ri-e s-ulfohyl *uior'ioiilfide to' the sodium benzene s uiiinate- V p f FRITZ W. H; REFERENCES CITED The renewing references are of record in" the file of this patent:

UNIT-ED 'STATESPATENTS' umb v Name 7 Date 1,673,522 Matthies et a1 June 12, 192B Zn-57,764 Blllrlken Oct. 20, 1936 

